white blood cell

Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

n. Any of various blood cells that have a nucleus and cytoplasm, separate into a thin white layer when whole blood is centrifuged, and help protect the body from infection and disease. White blood cells include neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Also called leukocyte, white cell, white corpuscle.

from Wiktionary, Creative Commons Attribution/Share-Alike License

n. A type of blood cell that is involved with an immune response, or part of the immune system.

from the GNU version of the Collaborative International Dictionary of English